The present invention relates to monospecific or bispecific antibody molecules that specifically bind antigens of Death Receptors, which are members of the tumor necrosis factor (TNF) receptor Superfamily (TNFR-SF) with an intracellular death domain. The invention relates in particular to antibody molecules of the IgG1 isotype having a mutation in the Fc region that enhances clustering of IgG molecules after target binding. The invention further relates to a combination of antibody molecules binding different epitopes on one or more specific Death Receptors. The invention also relates to pharmaceutical compositions containing these molecules and the treatment of cancer using these compositions.